Composition and process for removing moisture from hydrogen halides

ABSTRACT

A composition comprising a magnesium halide coated macroporous carbonaceous substrate is provided for effecting moisture removal from a hydrogen halide fluid. Moisture removal is effected by intimately contacting the hydrogen halide fluid with the magnesium halide coated macroporous carbonaceous substrate and separating the fluid from the coated substrate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a composition and process for removingmoisture from a hydrogen halide.

[0003] 2. Description of the Prior Art

[0004] At the present time, gaseous and liquid hydrogen halides areutilized as high purity anhydrous compositions. Anhydrous hydrogenhalides are commonly used in the semiconductor industry such as forcleaning reactor tubes and susceptors and as an etchant formanufacturing microcircuits.

[0005] In such applications, highly efficient water vapor or liquidremoval from hydrogen halides such as hydrogen chloride is requiredbefore its introduction to the end-use environment. Hydrogen chloride isnormally a gas and sometimes is transported, under pressure, as aliquid. Hydrogen chloride becomes a liquid at 615 psig. Water-containinghydrogen chloride is highly corrosive in character, and thus willnecessitate frequent replacement of piping, manifolds, valves, etc.,with which it comes into contact. In cleaning susceptors, i.e., thesupport structures on which wafers are processed, the presence of waterin the hydrogen chloride will result in the formation of new oxides onthe susceptor, thus opposing the cleaning function which is sought to becarried out. In etching applications, water-containing hydrogen chlorideis a source of undesirable moisture contamination in the semiconductormanufacturing environment, which may render the microcircuitry chipproducts made in such an environment deficient or even useless for theirintended purpose.

[0006] Among the methods which have been utilized by the prior art forremoving water from hydrogen chloride is the use of moisture-sorptivemolecular sieves. The difficulty of employing such methods forproduction of high-purity hydrogen chloride is that hydrogen chloride iscompetitive with water for the absorption sites on the molecular sieves.As a result, it is not possible to obtain the necessary lower residualwater values, on the order of 10 parts per million by volumeconcentration and less, in the effluent from the molecular sievecontacting step.

[0007] Hydrogen chloride has also been treated with sulfuric acid orphosphoric acid to produce dehydrated hydrogen chloride. Suchdehydration methods, however, have the associated disadvantage that theyadd sulfur or phosphorous to the hydrogen chloride, and these addedelements are highly undesirable contaminants in the aforementionedsemiconductor manufacturing applications.

[0008] It has also been proposed to utilize magnesium chloride supportedon alumina to effect removal of moisture from a hydrogen halide. It hasbeen found that this purifying material is undesirable when contactedwith high pressure hydrogen chloride such as in its liquid form sincealuminum reacts with the hydrogen chloride to form aluminum trichlorideparticles which clog filters through which the hydrogen chloride ispassed to effect its purification.

[0009] In addition, the formation of magnesium chloride on aluminainvolves multiple reaction steps wherein the alumina is first coatedwith a solution, e.g., 15% by weight of dibutylmagnesium in hexanesolvent. The solvent is removed by evaporation while heating. Thedibutylmagnesium is converted to magnesium hydride on alumina by heatingto about 250° C. The magnesium hydride then is converted to magnesiumchloride on alumina with concentrated hydrogen chloride. Thiscomposition then is used to remove moisture from hydrogen halides.

[0010] Hydrogen bromide is another example of a hydrogen halide which isrequired in essentially completely water-free condition in thesemiconductor manufacturing field. Hydrogen bromide is used in theelectronics industry as an etchant for wafers, and as a cleaning agentfor susceptors. In these applications, the presence of water impurity inthe hydrogen bromide will result in the same disadvantages notedhereinabove in connection with hydrogen chloride in similarapplications. In addition, when hydrogen bromide is used as an etchantfor wafers, hazing has been found to result when the hydrogen bromidecontains even minute amounts of water vapor.

[0011] The art has attempted to achieve removal of water from hydrogenbromide by the use of phosphoric acid as a drier. This method, whilegenerally useful to remove the water contaminant, nonetheless has theattendant disadvantage that it adds phosphorous to the hydrogen bromide,which as indicated above in connection with hydrogen chloride, is asignificant contaminant in the semiconductor manufacturing process.

[0012] Accordingly, it would be desirable to provide a composition andprocess for removing moisture from hydrogen halides and which does notproduce a contaminating by-product such as particles. In addition, itwould be desirable to provide such a composition and process which has ahigh capacity for removing moisture from hydrogen halides either ingaseous or liquid form. Furthermore, it would be desirable to providesuch a composition which can be formed from a simplified process ascompared to presently available processes for forming analogouscompositions.

SUMMARY OF THE INVENTION

[0013] This invention provides a composition for removing moisture froma hydrogen halide fluid comprising a macroporous carbonaceous supportupon which is deposited a magnesium halide which is either magnesiumchloride or magnesium bromide. The magnesium halide is deposited on thesurface of the macroporous carbonaceous support for first admixing thesupport with a solution of dibutyl magnesium in order to coat thesurfaces of the support with dibutyl magnesium. The solvent forming thesolution then is removed by evaporation in a non-reactive environment.Thereafter, the coated support is contacted with hydrogen halide fluidto convert the dibutylmagnesium to the magnesium halide. This processavoids the need for forming magnesium hydride.

[0014] In use, the support coated with magnesium halide is intimatelycontacted with a hydrogen halide fluid to effect substantially completeremoval of moisture from the hydrogen halide fluid. The halide of thehydrogen halide fluid and of the magnesium halide must be the same toprevent contamination of the fluid.

BRIEF DESCRIPTION OF THE DRAWING

[0015]FIG. 1 illustrates the use of the present invention.

[0016]FIG. 2 is a graph of a Foerier Transform Infra Red spectraillustrating the water removal capacity from nitrogen of the compositionof this invention.

[0017]FIG. 3 is a graph of a Foerier Transform Infra Red spectraillustrating the water removal capacity from HCl of the composition ofthis invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0018] The composition of this invention comprises a macroporouscarbonaceous support having an average pore size greater than about 100Angstroms up to about 100 μm, preferably between about 20 A and about1000 A which is coated with magnesium halide. Suitable carbonaceoussupports are formed, for example, by pyrolyzing polymeric resins.Representative suitable supports are formed by pyrolyzing sulfonatedstyrene/divinylbenzene macroreticular ion exchange resin and aredisclosed, for example, by U.S. Pat. No. 5,094,754, which isincorporated herein by reference. Such carbonaceous supports areavailable from Rohm and Haas Company, Philadelphia, Pa. under theregistered trademark AMBERSORB®.

[0019] The magnesium halide coating is formed on the particulatemacroporous carbonaceous support by first intimately contacting thesupport with a solution of a dialkyl magnesium compound such asdimethyl, diethyl, dibutyl or dipropyl magnesium, preferably dibutylmagnesium. Representative suitable solvents for forming the solutioninclude hexane, heptane or the like. Contact of the support and thesolution typically is effected for a time between about 1 hour and about4 hours, at a temperature between about 25° C. and about 70° C. Theresultant coated support is separated from the solution and excesssolvent is removed therefrom such as by evaporation. Evaporation can beeffected by heating such as to a temperature between about 55° C. andabout 65° C. in an inert or nonreactive atmosphere such as nitrogen oran inert gas.

[0020] In a final step, the coated support is contacted with a hydrogenhalide gas either alone or in a non reactive carrier gas such asnitrogen wherein the hydrogen halide comprises between about 5% and 100%volume percent of the gas. In this final step, the dialkyl magnesium isconverted to magnesium halide Hydrogen chloride is utilized as thehydrogen halide when the coated support is used to dry hydrogen chloridefluid. Hydrogen bromide may be utilized as the hydrogen halide when thecoated support is used to dry hydrogen bromide fluid. Contact with thehydrogen halide fluid is effected for a time and at temperature whereinsubstantially complete conversion of the dialkyl magnesium to themagnesium halide is effected. Typical contact times are between about1.1 min/ml of resin and about 5.5 min/ml of resin, preferably betweenabout 1.6 min/ml and about 5.5 min/ml. Typical reaction temperatures arebetween about 25° C. and about 240° C., preferably between about 40° C.and about 60° C.

[0021] The compositions of this invention are capable of removingmoisture from a hydrogen halide fluid even at high pressures wherein thefluid is a liquid without formation of reactive products such asparticulate reaction products which contaminate the hydrogen halide. Inaddition, the compositions of this invention are capable of withstandinghigh pressure liquid halide up to a pressure of about 1100 psig at 50°C.

[0022] The magnesium halide coating is sufficient to render thecomposition of this invention useful for removing moisture from ahydrogen halide fluid to less than about 100 ppb, preferably less thanabout 50 ppb but without significantly blocking the support macropores.The compositions of this invention are characterized by a moistureabsorption capacity in excess of about 40 liters of water per liter ofcoated support, preferably in excess of about 60 liters of water perliter of coated support. The concentration of magnesium halide exceedsat least about 0.1 moles of magnesium halide per liter of carbonaceoussupport, preferably in excess of at least about 1.2 moles of magnesiumhalide per liter of carbonaceous support.

[0023] In use, the composition of this invention is intimately contactedwith a fluid hydrogen halide either as a flowing fluid stream orquiescent in a container for the hydrogen halide in a manner so thatsubstantially all of the hydrogen halide contacts the composition.

[0024] Referring to FIG. 1, hydrogen halide fluid to be dried isintroduced into inlet 10 of housing 12. The fluid is passed through aretaining frit 14 and into the bed 18 of the coated carbonaceousparticles of this invention wherein moisture is removed from the fluid.The fluid then is passed through filter IS and out outlet 20 to a siteof use (not shown).

[0025] The following examples illustrate the present invention and arenot intended to limit the same:

EXAMPLE I

[0026] This example illustrates a method for making the magnesiumchloride coated product of this invention.

[0027] Two hundred (200) ml of Ambersorb® 563 carbonaceous adsorbent arecleaned in 200 ml of a 10% methanol/water solution. Ambersorb® 563 isavailable from Rohm and Haas Company, Philadelphia, Pa. and has asurface area of 550 m²/g and a macroporosity of 0.23 ml/g as measured bynitrogen porosimetry. The solution is poured off and the beads arerinsed three more times with methanol. The support is air dried untilfree flowing and then put into a 1000 ml cylinder with N₂ entering fromthe bottom while the cylinder is heated to 100° C. for about 4 hoursuntil most of the bulk water/methanol solution has been removed at whichpoint the cylinder temperature is raised to 240° C. for 15 hours. At theend of this activation period the support is cooled to 60° C. Enough 15%dibutyl magnesium in heptane solution is added to fill the void volumeof the carbon and then nitrogen flowing from the bottom of the cylinderis used to blow off 75% of the heptane. This step is repeated until allthe dibutyl magnesium in heptane has been added. Stirring is required toachieve a homogeneous mixture and prevent caking. The dibutyl magnesiumon the Ambersorb® 563 carbonaceous adsorbent is kept under a 1 slpmnitrogen stream at 55° C. for a full day and subsequently thecarbonaceous adsorbent is isolated, brought into a glove box and put ina sample cylinder appropriate for hazardous gas handling. The gas samplecylinder with the carbonaceous adsorbent is connected to a gas manifoldcapable of flowing both anhydrous HCl and dry nitrogen. A two foldexcess of 5% HCl in nitrogen and 15 psia and 1000 sccm is passed overthe carbonaceous adsorbent at which point pure HCl at 15 psia and 1000sccm is then passed over the carbonaceous adsorbent for 30 minutes andthe vessel is then pressurized to 60 psig with HCl overnight. Thecarbonaceous adsorbent is purged with 1000 sccm N₂ the following morningand the sample cylinder is heated to 240° C. for 52 hours. This purgingwould be more effective with high pressure CO₂. The final product emitsless than 1 ppm total hydrocarbons at 26° C.

EXAMPLE II

[0028] This example illustrates the use of the product of this inventionfor removal of moisture from nitrogen and HCl.

[0029] Tests were performed to determine whether the coated carbonaceousadsorbent can dessicate a nitrogen gas stream. To test water retention,N₂ or HCl gas at 500 sccm is dried with a conventional hydrogen halidepurifier. The HCl gas then is either passed through the purifierapparatus illustrated in FIG. 1 or can bypass the purifier. The bypassstream is representative of the background water level. The resultantgas stream is directed to a 10 meter path length gas cell kept at 130°C. for use with a Fourier Transform Infrared analysis apparatus (FT-IR).Four (45) PPM water in 100 sccm N₂ is added to the gas stream (for atotal flow of 600 sccm) on demand.

[0030] The composition of the FT-IR spectrum exhibits the ability toremove water moisture from N₂ to levels less than 100 ppb. FIG. 2 showsthree FT-IR spectra at 1772 cm⁻¹ to illustrate the water retentionability of the composition of this invention in N₂.

[0031] N₂ dried by the conventional purifier and which bypasses thecomposition of this invention is denoted “Dry N₂”. “Water” refers to thewet (4 PPM) N₂ gas stream which bypasses the composition of thisinvention and “New purifier+Water” refers to the wet N₂ passed throughthe composition of Example I. It is evident from the spectra that thereis no difference between “Dried N₂” and “New purifier+Water” indicatingthat the conventional purifier and the purifier of this invention arecapable of retaining water to the same level in N₂ (<100 ppb).

[0032] Referring to FIG. 3, the composition of Example I exhibits theability to remove water moisture from HCl to levels less than 100 ppb.FIG. 3 shows three FT-IR spectra at 1772 cm⁻¹ to illustrate the waterretention ability of the composition of Example I in HCl.

[0033] HCl dried by the conventional purifier and which bypasses thecomposition of Example I is denoted “Dry HCl”. “Water” refers to the wet(4 ppm) HCl gas stream which bypasses the composition of Example I and“New purifier+Water” refers to the wet HCl passed through thecomposition of Example I. It is evident from the spectra that there isno difference between “Dried N₂” and “New purifier+Water” indicatingthat the conventional purifier and the composition of Example I arecapable of retaining water to the same level in HCl (<100 ppb).

1. A composition suitable for effecting removal of water from a hydrogenhalide fluid which comprises a macroporous carbonaceous support coatedwith a magnesium halide.
 2. The composition of claim 1 wherein saidmagnesium halide is magnesium chloride.
 3. The composition of claim 1wherein said magnesium halide is magnesium bromide.
 4. The compositionof claim 1 having a water absorption capacity in excess of about 60liters of water per liter of said composition.
 5. The composition ofclaim 2 having a water absorption capacity in excess of about 60 litersof water per liter of said composition.
 6. The composition of claim 3having a water absorption capacity in excess of about 60 liters of waterper liter of said composition.
 7. The process for removing moisture froma hydrogen halide fluid which comprises intimately contacting said fluidwith a macroporous carbonaceous support coated with a magnesium halideand separating said fluid from said coated support.
 8. The process ofclaim 7 wherein said magnesium halide is magnesium chloride.
 9. Theprocess of claim 7 wherein said magnesium halide is magnesium bromide.10. The process of claim 7 wherein said hydrogen halide is a gas. 11.The process of claim 8 wherein said hydrogen halide is a gas.
 12. Theprocess of claim 9 wherein said hydrogen halide is a gas.
 13. Theprocess of claim 7 wherein said hydrogen halide is a liquid.
 14. Theprocess of claim 8 wherein said hydrogen halide is a liquid.
 15. Theprocess of claim 9 wherein said hydrogen halide is a liquid.